The overall aim of the proposal is to study the biochemical and physiological bases for the platelet abnormalities observed in patients with a wide variety of hemostatic defects. The project will study 1) In storage pool deficiency (SPD) (N=18) associated with heterogeneous defects in platelet Yield and dense granules, the nature of the granule defects (nucleotide and calcium transport, mepacrine and uranaffin studies) and their relation to the aggregation abnormalities, the pathogenesis of the secretion defect (role of ADP, abnormalities in prostaglandandin/TxA2 pathways), and contribution of platelet granules to platelet-subendothelial interaction. 2) In patients with primary secretion defects (N-15) who have been shown to have heterogeneous abnormalities in aggregation/secretion responses and TxA2 formation, the nature of these abnormalities through extensive studies on phospholipid and arachidonic acid (AA) metabolism (including stimulus-induced changes of phospholipid and 3H-AA metabolites (PA, TxB2, HHT, and HETE) and polyphosphoinositides, calcium mobilization, cAMP, energy metabolism, protein phosphorylation (including specific studies on possible abnormalities of 47K protein in granule extrusion), and possible cytoskeletal defects in resting and stimulated platelets. 3) In thrombasthenia (TSA) (N=5), possible defects in cytoskeletal proteins or assembly and the role of GPIIb-IIIa in mediating platelet adhesion. 4) In patients with new types of adhesion defects [different than the Bernard Soulier Syndrome (BSS)] the nature of the defect (contact vs spreading) utilizing appropriate flow conditions for maximizing defects in surface kinetics, and its possible basis, such as abnormalities in FVIII/VWF, glycoproteins and fibronectin. 5) Aspects of platelet procoagulant abnormalities, including possible defects of FVa binding in FXa-binding abnormality and the role of various platelet-related properties in coagulation by studying fibrin deposition and fibrinopeptide A release on subendothelium in patients with a variety of platelet disorders (FXa defect, TSA, BSS, SPD, and secretion defects) utilizing flow conditions in which differences between FVIII and FIX vs FXII and XI patients have been demonstrated. 6) In pseudo-von Willebrand's disease (and related disorders) possible defects in platelet glycoproteins, FVIII/VWF binding, platelet-subendothelial attachment, and possible therapy. 7) Utilizing a technique recently developed in our laboratory, primary hemostasis in a wide variety of patients with hemostatic defects by quantitative measurement of various bleeding time parameters and time-course studies on TxB2, 6-keto-PGF1alpha, PF4, and FPA.